1. Technical Field
The present invention relates to a liquid ejecting head for ejecting droplets from a nozzle in response to the displacement of a piezoelectric element, a liquid ejecting apparatus, and an actuator that includes a piezoelectric element.
2. Related Art
A representative example of liquid ejecting heads for ejecting droplets is an ink jet recording head. A typical ink jet recording head includes a piezoelectric element disposed on a flow passage forming substrate with a diaphragm interposed therebetween. The flow passage forming substrate includes a pressure generating chamber. The piezoelectric element includes a lower electrode, a piezoelectric layer, and an upper electrode. A displacement of the piezoelectric element generates pressure in the pressure generating chamber, allowing the ink jet recording head to eject ink droplets from a nozzle. It is known that the displacement characteristics of a piezoelectric element used in such an ink jet recording head depend greatly on the crystalline orientation of a piezoelectric layer. Thus, in some proposed piezoelectric elements, the crystals of a piezoelectric layer are appropriately orientated to improve the displacement characteristics (see, for example, JP-A-2004-66600).
In some piezoelectric elements that include a lower electrode, a piezoelectric layer, and an upper electrode, the piezoelectric layer tapers downward at its ends (tapered surfaces) (see, for example, JP-A-2007-118193).
In a piezoelectric element described in JP-A-2007-118193, although no upper electrode is formed on inclined end faces (hereinafter referred to as a tapered portion) of a piezoelectric layer, a lower electrode is continuously disposed across a plurality of piezoelectric elements. Thus, the tapered portion of the piezoelectric layer undergoes a strong driving electric field and may be damaged.
In piezoelectric elements described in JP-A-2004-66600 and JP-A-2007-118193, a lower electrode is continuously disposed across a plurality of piezoelectric elements. In other piezoelectric elements, a lower electrode is patterned for each piezoelectric element, and a piezoelectric layer extends to the outside of the lower electrode (for example, JP-A-2000-32653).
In a piezoelectric element described in JP-A-2000-32653, a tapered portion of a piezoelectric layer does not undergo a strong driving electric field and may not be damaged by the driving electric field. However, when a piezoelectric layer described in JP-A-2004-66600 is applied to a piezoelectric element described in JP-A-2000-32653 to improve the displacement characteristics of the piezoelectric element, the piezoelectric layer may be damaged around an end of a lower electrode during the operation of the piezoelectric element probably because of a difference in crystallinity between one portion of the piezoelectric layer on the lower electrode and the other portion of the piezoelectric layer outside the lower electrode (on a diaphragm). Furthermore, the piezoelectric element may have a low response speed and may be difficult to drive at a high speed.
Such problems may occur not only in ink jet recording heads for ejecting ink droplets, but also in other liquid ejecting heads for ejecting droplets and actuators that include a piezoelectric element.